In recent years, there have been increasing demands for the characteristics of photographic silver halide emulsions and, in particular, the demands have been highly leveled up for the photographic characteristics such as high sensitivity, low fogging and high gamma.
It has become essential to provide stable photographic characteristics against the variations in photographic conditions. In particular, it has been strongly demanded to make both sensitivity and contrast stable against the variations of various factors required in processing steps, such as the quantity of light-sensitive materials to be processed, the amount of a developer to be replenished, a temperature of the developer to be used and a processing time to be taken.
To meet these demands, there have been the proposals for highly sensitive emulsions having a high silver iodide content inside of the grains and a distinct core/shell structure in the grains thereof. These proposals were disclosed in, for example, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 143331-1985, 3247-1987 and 7039-1987.
With these emulsions, the developability thereof are not so good because a total average of silver iodide contents is relatively high and the contrasts may hardly be controlled within a certain developing time. Besides the above, there has also been a proposal for a silver halide emulsion in which a total average of silver iodide contents is lowered by reducing the silver iodide content of each core as the distinct core/shell structure remains unchanged. This proposal was disclosed in one of the examples given in Japanese Patent O.P.I. Publication No. 143331-1985. However, this emulsion deteriorates its pressure resistance property, though its development activity may be improved.
On the other hand, Japanese Patent O.P.I. Publication Nos. 35726-1985 and 147727-1985 disclose the technologies in which a high silver iodide content is provided to the cores of core/shell emulsion grains so as to reduce the total average silver iodide content of the emulsion. However, this emulsion has not any distinct core/shell-structure and, therefore, a high sensitization may hardly be achieved.
In the conventional technologies, as mentioned above, it has been difficult to materialize a silver halide emulsion which is excellent in development activity and ready in contrast control, without detriorating both sensitivity and pressure resistance property.